US20160126504A1 - Electroluminescent devices - Google Patents
Electroluminescent devices Download PDFInfo
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- US20160126504A1 US20160126504A1 US14/896,120 US201414896120A US2016126504A1 US 20160126504 A1 US20160126504 A1 US 20160126504A1 US 201414896120 A US201414896120 A US 201414896120A US 2016126504 A1 US2016126504 A1 US 2016126504A1
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- H—ELECTRICITY
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- H10K50/00—Organic light-emitting devices
- H10K50/30—Organic light-emitting transistors
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- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
- G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
- G09G3/3225—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
- G09G3/3258—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix with pixel circuitry controlling the voltage across the light-emitting element
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
- G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
- G09G3/3266—Details of drivers for scan electrodes
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/80—Constructional details
- H10K50/85—Arrangements for extracting light from the devices
- H10K50/856—Arrangements for extracting light from the devices comprising reflective means
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
- H10K59/121—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements
- H10K59/1213—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements the pixel elements being TFTs
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
- H10K59/121—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements
- H10K59/1216—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements the pixel elements being capacitors
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
- H10K59/131—Interconnections, e.g. wiring lines or terminals
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- H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
- H10K71/10—Deposition of organic active material
- H10K71/16—Deposition of organic active material using physical vapour deposition [PVD], e.g. vacuum deposition or sputtering
- H10K71/164—Deposition of organic active material using physical vapour deposition [PVD], e.g. vacuum deposition or sputtering using vacuum deposition
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- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2300/00—Aspects of the constitution of display devices
- G09G2300/04—Structural and physical details of display devices
- G09G2300/0404—Matrix technologies
- G09G2300/0408—Integration of the drivers onto the display substrate
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- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2300/00—Aspects of the constitution of display devices
- G09G2300/04—Structural and physical details of display devices
- G09G2300/0421—Structural details of the set of electrodes
- G09G2300/0426—Layout of electrodes and connections
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2300/00—Aspects of the constitution of display devices
- G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
- G09G2300/0809—Several active elements per pixel in active matrix panels
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0626—Adjustment of display parameters for control of overall brightness
Definitions
- the present invention relates to light emitting devices, especially transistors which incorporate an organic electroluminescent (EL) element to form an organic light emitting diode (OLED) in the transistor, and methods of manufacturing such devices.
- EL organic electroluminescent
- OLED organic light emitting diode
- An exemplary OLED display panel having an active matrix structure comprises a matrix of pixel circuits.
- Each pixel circuit has an OLED device and backplane having matrix wiring and thin film transistors (TFTs) for switching and driving the OLED device.
- TFTs thin film transistors
- Such a pixel circuit has difficulty delivering and controlling electric current passed through each OLED device. This is because each drive TFT is comprised of amorphous silicon (a-Si) which has low carrier mobility. The low carrier mobility prevents a small a-Si TFT from delivering a large drive current. Additionally, such an a-Si TFT suffers from great changes in characteristics when subjected to a continuous current application, making control of the drive current difficult.
- a-Si amorphous silicon
- a first proposed solution is to use a polycrystalline silicon TFT for the drive TFT.
- This provides the drive TFT with higher carrier mobility.
- this technology necessitates crystallization annealing processes in order to obtain polycrystalline silicon, generally on a glass substrate.
- the crystallization annealing is typically conducted through laser heating to temperatures above 1000° C., and it suffers from the disadvantage of a lower throughput as well as lower yield, resulting in a significantly higher cost as compared with a-Si TFT.
- a second proposed solution is to use amorphous oxide TFTs for the drive TFTs.
- This technology uses a non-crystalline semiconductor of metal oxide, such as an oxide of In or Zn, and accordingly has an advantage of eliminating the necessity for crystallization processes such as a laser annealing process.
- this technology also suffers from the disadvantage of significantly lower yield. The low yield is due to a need for approximately 5-micron rule micromachining. There is also a difficulty in using existing a-Si manufacturing lines to manufacture amorphous oxide TFTs.
- a third proposed solution is to provide a luminescence transistor by giving the TFT a luminescence function, thereby reducing the number of transistors required in the pixel circuit.
- An example of such an attempt is disclosed in JP2002-246639 where the TFT has a luminescence signal visible as a narrow line on a surface.
- the TFT has a luminescence signal visible as a narrow line on a surface.
- Narrow line emission has limited scope in applications involving display units. Further, it is difficult to separate the luminescence transistor manufacturing process and the backplane manufacturing process.
- a fourth proposed solution is to provide a luminescence transistor that operates based on function as a junction transistor, as opposed to a TFT, which is a field effect transistor.
- a TFT which is a field effect transistor.
- a luminescence transistor based on a junction transistor function may be more realistic than a TFT function because unlike a TFT, a junction transistor does not confine current to a narrow channel. Consequently, junction transistor technology can create a pixel having a greater luminescence area than in the case of TFT.
- Such technology is disclosed in JP2005-293980, JP2006-269323, JP2007-200788, JP2009-272442, and JP2010-135809. Disclosed amongst these documents is a current control base electrode disposed in a middle portion of an organic semiconductor layer, in which the base electrode is a slit-like conductor, a planar conductor, or a conductor/semiconductor having a laminated structure.
- the disadvantage of these technologies is that a semiconductor layer having a current control base electrode disposed in the middle portion is difficult to manufacture.
- This technology enables the use processes at lower temperatures (eg at or below 300° C.) than in some other technologies, for example in technologies requiring annealing. Such technology therefore has an advantage of allowing a separation between the luminescence transistor manufacturing process and the backplane manufacturing process.
- the structure of having a conductor inserted into an organic semiconductor performs poorly as a junction transistor. Furthermore, the structure is unstable, and its instability becomes an impediment to volume production and to production of large panels.
- Various embodiments of the invention may therefore provide a stable, inexpensive, and/or high-performance luminescence transistor or active matrix OLED display.
- Various embodiments may allow a separation between the luminescence transistor manufacturing process and the backplane manufacturing process, and/or reduce a current control load at the backplane.
- an electroluminescent device comprising: an organic electroluminescent element and a junction transistor having a first region, a second region, and an intermediate semiconducting region configured to control flow of charge between the first and second regions. At least two abutting regions consist essentially of one or more semiconducting inorganic metal compounds. Each region of the junction transistor and the electroluminescent element are successively stacked along a common direction.
- the electroluminescent device is a luminescence transistor.
- the luminescence transistor has preferably three electrodes, specifically a first electrode being connected to the intermediate region, a second electrode being connected to either the junction transistor or the electroluminescent element and a third electrode being connected to the other of the junction transistor or the electroluminescent element.
- the intermediate semiconducting region is a base region
- the first region is an emitter region
- the second region is a collector region
- the base region and at least one of the emitter region or collector region being abutting regions.
- the organic electroluminescent element is distinct from and, more preferably, abuts the junction transistor.
- one or more layers e.g. a conducting layer
- the electroluminescent element and the junction transistor may exist between, but electrically couple, the electroluminescent element and the junction transistor.
- the electroluminescent element and each region of the junction transistor are successively stacked along a vertical direction.
- the two abutting regions consist essentially of one or more semiconducting inorganic metal compounds selected from metal oxides, nitrides, sulphides or carbides.
- the intermediate and each of the first and second regions consists essentially of at least one semiconducting material.
- back-to back p-n junctions are respectively created between the first region and the intermediate region and between the intermediate region and the second region, thereby forming a PNP junction transistor or an NPN junction transistor.
- the intermediate semiconducting region is the base, and the first and second regions respectively form either (i) the emitter and collector, or (ii) the collector and emitter of the junction transistor.
- a schottky diode or schottky junction is additionally included between the intermediate region and the first region and/or between the intermediate region and the second region.
- the intermediate region and only one of the first and second regions consist essentially of semiconducting material, and the other of the first and second regions consists essentially of at least one metal forming schottky junction with the intermediate region.
- the first region consists essentially of one or more semiconductor materials selected from Zn, Cu, Ru, Al, In, Ga, Sn or Ti oxides.
- the electroluminescent device is configured such that light is generated from an organic light emission layer within the electroluminescent element, wherein the light emission layer is located between the junction transistor and further layers of the electroluminescent element.
- the further layers include a hole transport layer and/or an electron transport layer.
- the electroluminescent element further includes a hole injection layer or an electron injection layer.
- the electroluminescent element is referred to as being “organic” due to the organic light emission layer, but the element can nonetheless include inorganic layers.
- the element may include an inorganic electron injection layer, such as LiF.
- the electroluminescent element is or includes an organic light emitting diode.
- the organic electroluminescent element forms only part of an organic light emitting diode, with the other part of the organic light emitting diode being provided by the junction transistor, eg the collector of the junction transistor.
- light generated from the light emission layer is transmitted through the junction transistor and is reflected by one or more of the further layers of the organic electroluminescent element.
- light generated from the light emission layer is transmitted through the further layers of the organic electroluminescent element and is reflected by a reflector region located between the junction transistor and a substrate.
- light generated from the light emission layer is transmitted through the junction transistor as well as the further layers of the organic electroluminescent element.
- a pixel circuit comprising an electroluminescent device, according to the first aspect of the present invention, connected to a control circuit for controlling operation of the electroluminescent device, wherein the control circuit comprises: a switching means; a current setting transistor; and a capacitor.
- the switching means is configured to selectively couple a first control line and to an input electrode of the electroluminescent device for setting a voltage at the input electrode when the switching means is on; the current setting transistor is configured to deliver into or draw current out of the electroluminescent device, via said input electrode, when the current setting transistor is in a biased state; and the capacitor is configured to prolong the current setting transistor in the biased state when the switching means is turned off so as to prolong said delivered or drawn current.
- the current setting transistor is configured to deliver current into the electroluminescent device, whereas in the cases where the junction transistor is a PNP transistor, the current setting transistor draws current out of the electroluminescent device.
- the switching means is a thin film transistor (TFT) having a gate connected to a second control line and source and drain configured for said coupling of the first control line to the input electrode.
- TFT thin film transistor
- the current setting transistor is a TFT having a gate connected to the capacitor.
- the switching means additionally selectively couples the first control line to configure the current setting transistor in a biased state when the switching means is on.
- a second switching means selectively couples the first control line to set the voltage at the input electrode when the switching means is on, wherein the capacitor is isolated from the input electrode.
- a pixel circuit comprising an electroluminescent device according to the present invention connected to a matrix circuit for controlling operation of the electroluminescent device, wherein the pixel circuit comprises: a first control line coupled to an input electrode of the electroluminescent device for setting a voltage at the input electrode; and
- a second control line connected to the electroluminescent device for applying a voltage between an anode and cathode of the device; wherein the first and second control lines are synchronised such that the first control line provides a pulse that controls luminescence emitted from the electroluminescent device.
- a pixel matrix circuit comprises a plurality of said pixel circuits, wherein each electroluminescent device, wherein the second control lines of each pixel circuit are connected to a scan controller and the first control lines of each pixel circuit are also connected to a signal controller.
- a multiplexing drive for a pixel matrix circuit as described above comprises the signal controller and scan controller configured to independently control each pixel circuit.
- a multiplexing drive comprising: at least two of said pixel circuits according to the third aspect of the present invention, wherein the signal controller and scan controller of each circuit is arranged to operate independently.
- an electroluminescent display panel comprising: a front plane and a back plane, the front plane including at least an electroluminescent device according to the present invention, and the back plane including at least a control circuit including at least two TFTs and at least one capacitor.
- the TFTs are chosen from polycrystalline Si TFT, amorphous Si TFT, oxide TFT or organic TFT.
- the at least two TFTs and the at least one capacitor are configured to form a pixel circuit in accordance with the third aspect of the present invention.
- a method for manufacturing an electroluminescent device in accordance with the present invention wherein the method includes:
- a seventh aspect of the present invention there is provided a method of manufacturing an electroluminescent display panel in accordance with the present invention, wherein the backplane is manufactured by at least a process of a first type and manufacturing the front plane includes a process of a second type that is different to the first process.
- the first type of process is performed at a temperature between 250-350 degrees C.
- the second type of process is performed at a substrate temperature below 200 degrees C.
- the substrate temperature is between room temperature and 100 degrees C.
- the second type of process is used to depositing one or more organic layers on, including at least the electroluminescent element, on the layers consisting of one or more semiconducting inorganic metal.
- the electroluminescent device is manufactured by a method in accordance with the sixth aspect of the invention.
- FIG. 1 is a diagrammatic view of an embodiment of an electroluminescence transistor comprising a PNP junction transistor
- FIG. 2 is a diagrammatic view of an embodiment of an electroluminescence transistor the same as in FIG. 1 , but having a base comprised of multiple layers;
- FIG. 3 is a diagrammatic view of another embodiment of an electroluminescence transistor comprising an NPN junction transistor
- FIG. 3A is a diagrammatic view of another embodiment of a PNP electroluminescence transistor in accordance with FIG. 1 or 2 , configured for bottom emission;
- FIG. 3B is a diagrammatic view of another embodiment of a PNP electroluminescence transistor in accordance with FIG. 1 or 2 , configured for top and bottom emission;
- FIG. 4 is a diagrammatic view of another embodiment of a PNP electroluminescence transistor as in FIG. 1 or 2 , but having a reflector and being configured for top emission;
- FIG. 5 is a diagrammatic view of an embodiment of an electroluminescence transistor comprising a NPN junction in accordance with FIG. 3 , configured for top emission;
- FIG. 6A shows a top view of an exemplary fabrication of a junction transistor in accordance with the present invention
- FIG. 6B shows a cross-sectional view of section A-A through the junction transistor of FIG. 6A ;
- FIG. 7A illustrates experimentally derived current-voltage curves for the respective p-n junctions of the junction transistor of FIG. 6A ;
- FIG. 7B illustrates experimentally derived current-voltage curves illustrating transistor characteristics of the junction transistor of FIG. 6A ;
- FIG. 8A shows a top view of an exemplary fabrication of a luminescence transistor in accordance with the present invention
- FIG. 8B shows a cross-sectional view of section A-A through the luminescence transistor of FIG. 8A ;
- FIG. 8C illustrates experimentally derived luminescence vs bias voltage curves illustrating luminescence characteristics of the luminescence transistor of FIG. 8A ;
- FIG. 9 shows an display panel having a grid of pixels driving electroluminescence transistors that are in accordance with the present invention.
- FIG. 10A shows an example of pixel circuit for driving a PNP electroluminescence transistor in accordance with an embodiment of the present invention
- FIG. 10B shows another example of pixel circuit for driving a PNP electroluminescence transistor in accordance with an embodiment of the present invention
- FIG. 10C shows an example of pixel circuit for driving an NPN electroluminescence transistor in accordance with an embodiment of the present invention
- FIG. 12 illustrates a portion of an active matrix circuit having two pixel circuits, each pixel circuit being in accordance with FIG. 10A , and being connected to the same signal line and different scan lines;
- FIG. 14 illustrates, for the portion of the active matrix illustrated in FIG. 12 , the current signal into the signal line and the brightness of light emitted from one of the pixel circuits, when the pixel circuit is iteratively pulsed in successive scan cycles;
- FIG. 15 shows an exemplary layout of a pixel for an active matrix display
- FIG. 18 is a schematic illustration of the semiconductor band structure of the electroluminescence transistor of FIG. 18 .
- Electroluminescent device in the form of electroluminescence transistor 100 consists of an electroluminescent (EL) element 12 stacked on a junction transistor 11 to form a structure of stacked laminae or layers (referred to herein as “laminated structure” 150 ).
- the laminated structure 150 sits flush upon substrate 1 , with each layer being substantially flat and overlying each other.
- Each layer is stacked successively on the preceding layer, so that each layer progresses the stack along a common direction that is generally orthogonal to a plane in which the preceding layer lies and to the plane in which the substrate lies.
- Such a configuration results is referred to as ‘vertical’ configuration because during manufacturing the substrate lies in the horizontal plane.
- the junction transistor 11 is comprised of a base 4 is sandwiched between an emitter 3 and collector 5 to form a stack of semiconductors.
- the junction transistor 11 may have a PNP, NPN, n-type only or p-type only configuration.
- P refers to a p-type semiconductor in which a hole functions as a primary carrier
- N refers to an n-type semiconductor in which an electron functions as a primary carrier.
- a junction structure in which these are alternately joined to one another so as to form three layers are referred to as “PNP” or “NPN”.
- the emitter 3 , base 4 , and collector 5 are respectively p-type, n-type, and p-type semiconductors, thus forming a PNP junction.
- the outer ends of the laminated structure 150 illustrated in FIG. 1 as bottom end 154 and top end 156 of the laminated structure 150 , respectively, are each in contact with electrodes 2 , 10 .
- the electrodes 2 and 10 provide the laminated structure 150 with electrical contacts to allow a voltage 158 to be applied across structure 150 .
- a current flows through each of the layers 3 - 9 when a second voltage 159 is applied to bias the base such that the base emitter junction is forward biased.
- electric current in terms of a notional positive charge
- flows into the emitter 3 and out of the electron injection layer 9 the electrode in contact with the emitter 3 acts as an anode
- the electrode 10 in contact with electron injection layer 9 acts as a cathode.
- Current is also drawn from the base 4 , but the current is small compared with the current flowing from the anode 2 to the cathode 10 .
- an NPN transistor current travels in an opposite direction to the PNP transistor.
- the base 4 In order to control the voltage of the base 4 , the base 4 needs to be (or include a layer that is) of low resistance, ie good conductivity (generally less than 100 k ⁇ /sheet). However, the conductivity of the base 4 tends to be adversely affected if the collector 5 is a metal oxide semiconductor. Therefore, it is advantageous for the collector 5 is in this embodiment consists of organic material, instead of an oxide semiconductor or other inorganic semiconductor. This organic material is also advantageously in contact with the EL element 12 .
- One organic semiconductor that is suitable for the collector 5 is TcTa.
- Other suitable organic semiconductors include NPD, TAPC, PDA, TPD and m-MTDATA.
- the base layer 4 of the junction transistor 11 consists of a structure where a low resistive layer (generally less than 100 k ⁇ /sheet) and at least one high resistive layer (generally greater than 1M ⁇ /sheet) are laminated to form two or more layers. More specifically, the base 4 B consists of three layers, in which a low resistive layer 14 is sandwiched between high resistive layer 13 , in contact with emitter 3 , and a high resistive layer 15 , in contact with collector 5 .
- the base layer is typically thinner than the emitter or collector, requiring interface control with the emitter or collector and at the same time proper conductivity. For this reason, a structure in which the low resistive layer and high resistive layer are laminated to form two or more layers is an effective option.
- junction transistor 11 is a PNP type transistor, as would be understood by a person skilled in the art, a small portion of the current that enters the emitter 3 will exit the base 4 , rather than the collector 5 .
- the junction transistor 11 B is an NPN type transistor, so in that in normal use, flows from the collector to emitter, with a small proportion of the total emitter current comprising a current component that flows into the base and out of the emitter.
- the electroluminescence transistor 100 B is a reciprocal the device in FIG. 1 , as the electric current is configured to flow in the opposite direction to that illustrated in FIG. 1 and FIG. 2 .
- the bottom face 153 of cathode 10 abuts substrate 1 , and a top face 155 of cathode 10 is forms a low resistance contact with the bottom side 154 of the laminated structure 150 B.
- Anode 2 forms a low resistance contact with the top side 156 of the laminated structure 150 B.
- the layers 6 - 8 of the EL element 12 B can be comprised of the same materials as layer 6 - 8 of EL element 12 , but with the layers being positioned in the an opposite order.
- the layers from the anode 2 to collector 5 B are therefore, successively, hole transport layer 6 , emission layer 7 and electron transport layer 8 .
- the anode 2 acts as the hole injection layer for the EL element 12 B
- the collector 5 B acts as the electron injection layer for the EL element 12 B.
- the collector 5 B, base 3 B, and emitter 2 B are respectively N-type, P-type and N-type semiconductors, thus forming a NPN junction transistor element 11 B.
- the junction transistor element 11 B is mostly inorganic and the N and P semiconductors may be comprised of the same materials as described in relation to EL device 100 .
- the N and P semiconductor materials are metal oxides as already described herein.
- the n-type emitter can be one or more metal oxides selected from Zn, Cu, Ru, Al, In, Ga, Sn or Ti oxides
- the p-type emitter can be one or more metal oxides selected from Zn, Cu, Ru, AL, In, Ga, Sn or Ti oxides.
- collector 5 B can also be a p-type metal oxide, as in the case of device 100 , it is more advantageous for the collector 5 B to be an organic semiconductor.
- Appropriate organic semiconductors for collector 5 B include TmPyPB, BPhene, PBD, TAZ, BND, OXD and TPBi.
- the junction transistor 11 E is an N-type only transistor.
- the base 4 E consists of a structure where a high resistive layer 300 (generally greater than 1M ⁇ /sheet) and a conductive or low resistive layer 302 (generally less than 100 k ⁇ /sheet) 302 laminated to form two layers, thus forming an N-type only junction.
- a suitable material for use in the high resistive layer 300 is high resistive ITO, whereas a suitable material for use in the conductive layer is conductive IGZO. [WHAT OTHER MATERIALS ARE SUITABLE?]
- the high resistive (insulating) layer 300 creates a potential energy barrier to the flow of charge between the emitter 3 and collector 5 . Adjusting the potential of the base 4 E enables that energy barrier to be overcome and the charge flow to be controlled.
- FIG. 18 depicts the semiconductor band structure of the electroluminescence transistor of FIG. 17 .
- electrons are transported in the highest occupied molecular orbit (HOMO) from the cathode 10 , and other electrons are transported in the conduction band from the anode 2 .
- Holes are generated at the PN junction of the interface of the hole transport layer (HTL) 6 and the hole injection layer (HIL) or collector 5 .
- the holes and electrons from the cathode 10 recombine in the emission layer 7 , resulting in the emission of light.
- the injected current can be regulated by controlling the potential of base electrode 4 E.
- the emitter may be formed from conductive ITO, InO, ZnO, IGZO, SnO. [WHAT OTHER MATERIALS ARE SUITABLE?]
- the junction transistor is a P-type only transistor
- the base consists of a structure where a high resistive layer and a conductive or low resistive layer laminated to form two layers, thus forming an P-type only junction.
- the emitter may be formed from conductive CuO, CuAlO [WHAT OTHER MATERIALS ARE SUITABLE?]
- the electrodes 2 , 10 are constructed of a material suitable for their roles interfacing with hole-injecting or electron-injecting semiconductors, or to provide the hole-injection (by the anode) or electron injection (by the cathode), at the bottom and top ends 154 , 156 of laminated structure 150 .
- the anode being on the hole-injection end, in some embodiments contains at least one of Ga, Zn, Cu, In, Ti, and Si metal oxide semiconductors.
- the cathode being at the electron injection end, in some embodiments contains at least one of Al, Li, Mg, K, Na, Ba, Sr, Ag, Ca and Cs metal or metallic compounds.
- Al Li, Mg, K, Na, Ba, Sr, Ag, Ca and Cs metal or metallic compounds.
- the use of these materials allows barrier height to be controlled when holes or electrons are injected.
- emitter 3 is an inorganic metal oxide semiconductor formed of CuAlO 2.
- the anode 2 attached to the emitter 3 is comprised of ITO (In, Sn oxide) or mainly ITO.
- ITO In, Sn oxide
- ITO In, Sn oxide
- ITO In, Sn oxide
- ITO In, Sn oxide
- ITO In, Sn oxide
- ITO In, Sn oxide
- ITO In, Sn oxide
- Al metal or mainly Al
- KF or LiF is used for an electron injection layer 9 .
- the Al cathode will reflect light generated from emission layer 7 .
- the substrate 1 is transparent to allow the generated light 160 to be emitted pass through it, as illustrated in FIG. 3A .
- substrate 1 has a light transmissibility of at least than 50 percent at light wavelength of 400 to 800 nm (ie covering the spectrum of visible light).
- the transistor element 11 is also transparent, and has a light transmissibility of at least 50 percent at light wavelength of 400 to 800 nm. Any light generated from the emission layer 7 of organic EL element 12 that is falls on cathode 10 is reflected by the cathode 10 and radiated through the glass substrate 1 . Therefore the emitted light 160 is radiated mainly through the transparent substrate.
- This arrangement is referred to as a bottom emission configuration.
- Such a structure allows the manufacture of organic EL element 12 to occur after the fabrication of the junction transistor 11 , thereby preventing the manufacturing processes of the junction transistor 11 from damaging the organic EL element 12 .
- the cathode can be made of a transparent material, such as a metal oxide (eg ITO) having transmissibility of at least 50% for visible light, rather than a reflective metal.
- a transparent material such as a metal oxide (eg ITO) having transmissibility of at least 50% for visible light, rather than a reflective metal.
- transistor 100 C in FIG. 3B this allows light to be emitted from both the top and opposite, bottom side of the transistor.
- the other components of transistor 100 C can be the same as transistor 100 .
- transistor 100 C can include, for example, LiF for the electron injection layer 9 , TcTa for the Collector 5 , ZnO—In for the Base 4 , CuAlO 2 for the emitter 3 , ITO for the anode 2 , and glass for the substrate 1 .
- the electroluminescence transistor can be configured to have light emitted only from the end of the electroluminescence transistor on the opposite end to the substrate (ie the top end), as illustrated in the embodiment illustrated in FIG. 4 (and FIG. 5 ).
- Such structures are referred to as top emission configurations.
- FIG. 4 illustrates an embodiment of an electroluminescence transistor 100 A having the same features as described in relation to electroluminescence transistor 100 C of FIG. 3B , except that the substrate end of the device 100 A is reflective rather than transparent, so that light is radiated mainly through transparent cathode 10 .
- the reflectivity at the substrate side is provided by a chromium reflector 46 between the substrate 1 and anode 2 .
- FIG. 5 Another embodiment of a top emission configuration is illustrated in FIG. 5 for an NPN luminescence transistor 100 B consistent with FIG. 3 .
- a reflecting surface is provided on the transistor or substrate side of the EL element 12 .
- luminescence transistor 100 B does not require a separate reflector layer.
- the junction transistor electrode (cathode 10 ) in contact with the substrate is a reflective metal, such as aluminium.
- the anode 2 at the end opposite the substrate is a transparent material such as an a metal oxide semiconductor (eg ITO), thus allowing light to be emitted primarily from the top of the device 100 B.
- ITO metal oxide semiconductor
- Junction transistor 11 C has an anode 21 of ITO having a film thickness of about 150 nm, and a base contact 26 .
- the anode 21 and base contact 26 are formed on a glass substrate 20 .
- Emitter 22 is a P-type CuAlO 2 film having a film thickness of about 80 nm, which is formed by sputtering on the anode 21 . Due to the use of a stencil mask, the area of the film that comprises base 23 is limited in area, which limits current from straying laterally and also limits the luminescence region of the substrate 20 (ie, the region from which light is emitted from the bottom 164 of the substrate 20 ) to a middle portion of the substrate, ie the portion of the substrate 20 that is covered by base 23 .
- Base 23 is formed so as to cover the luminescence region and be in contact with the base contact 26 .
- the base is a comprised of three n-type layers consisting of a lower resistive ITO layer 28 sandwiched between lower and upper high resistive ZnO layers, 27 and 29 , respectively.
- Each of the ZnO layers 27 , 29 have a film thickness of 15 nm, while the ITO layer 28 has a film thickness of 5 nm.
- the base layers 27 - 29 are formed by successively sputtering each layer, using a stencil mask. Changing the film thickness of the ITO layer 28 allows the conductivity of the base 23 to be adjusted.
- an top electrode 25 comprised of gold is vacuum-deposited.
- the film thickness of the top electrode 25 is about 100 nm.
- FIG. 7A shows current-voltage characteristics for the respective p-n junctions formed between the emitter 22 and base 23 , and between the collector 24 and base 23 .
- a voltage V EB was applied from the emitter 22 to base 23 (ground), via the anode 21 and base contact 26 electrodes, respectively.
- the anode 21 and the base contact 26 the same voltage as the emitter 22 and base 23 , respectively, due to low resistance contact between the electrodes 21 , 26 and their respective semiconductors 22 , 23 .
- V EB is indicated along the x-axis as bias voltage 66 , measured in volts.
- FIG. 7B illustrates the results of an experiment in which transistor characteristic curves were derived from operation of junction transistor 11 C.
- the y-axis indicates current, in milliamps, from emitter 22 to collector 24 with respect to bias voltage from emitter 22 to 24 on the x axis. Characteristics curves are illustrated for six different base currents ranging from 0 to ⁇ 1.0 ⁇ A, the negative base current indicating that current is leaving the transistor 11 C out of base 23 .
- the voltage V EC was applied to measure the dependence of a current I EC on base current I B , showing that the current between the emitter 22 and collector 24 modulates, depending on the base current I B .
- an electron transport layer 37 is provide by vacuum depositing TmPyPB, with a film thickness of about 20 nm, over layer 36 .
- an electron injection layer 38 consisting of LiF, with a film thickness of about 1 nm
- cathode 39 consisting of Al having a film thickness of about 100 nm
- the stencil mask is configured to allow the cathode 39 to be formed such that it extends beyond the luminescence region so to provide an outside electrode portion 39 D ( FIG. 8A ).
- FIG. 9 depicts an active matrix organic light emitting diode display (AMOLED) 201 comprised of a grid of pixels 201 A.
- Each pixel includes three pixel circuits, described below, with each circuit having an electroluminescent element in accordance with the present invention (eg electroluminescence transistor 100 ), respectively configured to emit light in red, green and blue light.
- Each pixel circuit is addressed by a unique intersection of horizontal scan lines 219 a (r, g, b) to 219 n (r, g, b) and vertical signal lines 218 a (r, g, b) to 218 n (r, g, b).
- Each of the red, green and blue light pixel circuits could be considered sub-pixels of a single pixel. However, for convenience, no distinction is made hereinafter between pixels and sub-pixels—both are referred to as ‘pixels’.
- Circuit 200 A includes a luminescence transistor 202 such as luminescence transistor 100 , or any other p-n-p type electroluminescent transistor in accordance with the present invention.
- a luminescence transistor 202 such as luminescence transistor 100 , or any other p-n-p type electroluminescent transistor in accordance with the present invention.
- the current through the luminescent element is a function of a base current I B into or out of base 208 .
- the junction transistor element of the luminescence transistor is a PNP-type junction transistor, when base current I B is out of the base 208 when the luminescence transistor is on. Since the junction transistor is a PNP-type, the luminescence transistor 202 will turn on when the voltage of base 208 is pulled low (toward the ground line 212 ), and will be off when the voltage of base 208 is pulled high (toward the power line 210 ).
- TFT 221 When the signal line 218 a is low and the scan line 219 a is high, TFT 221 is on, pulling the base voltage low drawing current though the base. The current through the base generates a voltage between the emitter and base, which is held by a capacitor.
- the capacitor 220 In FIGS. 10A and 10B , the capacitor 220 is connected between the base 208 and the power line 210 . The voltage at the base will settle to a pre-determined steady-state level, determined by the voltage of the signal line, thereby resulting in a predetermined current through the electroluminescent element of the luminescence transistor 202 . Thus results in the emission of light at a predetermined intensity or brightness.
- the precise current drawn from base 208 is largely determined by a current setting transistor 222 which has its gate and either its source of drain coupled to the base 208 , which the other of the source or drain being connected to ground line 212 .
- the current setting transistor 222 thus acts as a current source, pulling current from the base 208 to ground.
- TFT 221 When the scan line 219 a is pulled high, TFT 221 turns off. However, the capacitor 220 keeps the voltage that the gate of current setting transistor 222 is a biased state such that the same level of current continues to be pulled from base 208 , and therefore the predetermined illumination level of the luminescence transistor 202 .
- the capacitor 220 will gradually discharge due to the resistance between base 208 and the anode 206 of the luminescence transistor 202 , connected across the capacitor 220 .
- the base voltage will gradually increase until the electroluminescent transistor turns off on the current setting transistor is no longer draws current from the base 208 .
- the presence of the capacitor prolongs the on-time of the transistor 202 , compared to the same circuit without the capacitor.
- An alternative exemplary pixel circuit 200 B ( FIG. 10B ) is the same as pixel circuit 200 A, except that the switching transistor 221 that is connected to the base of the electroluminescent device is disconnected from the capacitor and current setting transistor.
- a second switching transistor 223 independently couples the signal line to the capacitor and the gate of the current setting transistor. In this manner, when the scan line goes high and switching transistors 221 and 223 turn off, the capacitor does holds its charge for much longer because it is isolated from the base of the luminescence transistor and has no other low resistance discharge path.
- the configuration in FIG. 10B can be summarised as providing a pixel configuration constituting a display that includes the luminescence transistor, at least two thin-film transistors, and at least one capacitor and holds the gate voltage of one of the thin-film transistors through the electric voltage generated by an electric current that is passed through the base of the luminescence transistor and thereby gives a predetermined brightness, wherein the source or gate electrode of the thin-film transistor is connected to the base layer of the luminescence transistor, and one terminal of the capacitor is connected to the gate electrode of the thin-film transistor, and the gate voltage of the thin-film transistor is determined by a voltage given from a signal line, and, at the same time, is held by electrical charge stored in the capacitor and, in addition, an electric current flowing through the base layer of the luminescence transistor is held, thereby setting a predetermined brightness.
- the gate voltage of current control transistor is set by an electric voltage that is generated between the base and the emitter of the luminescence transistor as a result of the current passed through the base of the luminescence transistor.
- the luminescence transistor can thereby be biased to give a predetermined brightness level.
- a predetermined brightness level is set in the luminescence transistor and held until a new brightness level is set by the voltage level of the signal line, at the next scan cycle.
- JP2008-171580 discloses a pixel circuit in which a luminescence transistor is driven by one or two TFTs, but in contrast with the pixel circuit in FIG. 10A , the pixel circuit cannot hold the gate voltage of the thin-film transistor through the electric voltage generated by an electric current that is passed through the base.
- the above pixel circuits can be modified to operate on an n-p-n type luminescence transistor (eg luminescence transistor 100 B), as illustrated in FIGS. 10C and 10D .
- the functions of each of the circuit components is the same as in FIGS. 10A and 10B , but with some variations in the topology.
- the emitter of the luminescence transistor is on the ground line side of the circuit of the circuit, as opposed to the power line side in the p-n-p case.
- the luminescence transistor turned on by pulling its base electrode high.
- the positions of the capacitor and the current setting resistor are revered compared to the p-n-p case, such so in the n-p-n case the capacitor is connected between the base and ground and the current setting transistor is located between the base and the power line.
- the luminescence transistor is turned on when the signal and scan lines are high, driving current into the base.
- the luminescence transistor is off, when the scan line is low.
- the pixel circuit of FIGS. 10A, 10B, 10C and 10D is formed such that the active capacitors, switching transistor(s) and current setting transistor are formed in a planarization layer 18 ( FIG. 11 ) on a substrate 1 .
- the substrate 1 can be transparent under visible light so that light can be transmitted through the substrate (eg a bottom emission configuration).
- This structure has an advantage of enabling a separation between the manufacturing process of a backplane layer 16 having the switching and current setting TFTs (only one TFT 19 is shown), the capacitor (not shown) and matrix wiring, and the manufacturing process of a separate layer 17 having the luminescence transistor.
- the backplane layer includes, for example only one TFT (ie switching transistor 221 ), as shown in FIG. 11 , rather than the two or three transistors and a capacitor as in the pixel circuits of FIGS. 10A-10D .
- planarization of the backplane his is particularly beneficial because, the backplane can be manufactured using existing manufacturing facilities, so investment is only required to develop manufacturing facilities for the luminescence transistor itself.
- the thin-film transistor includes an active layer consisting mainly of non-crystalline silicon or metal oxide.
- the thin-film transistor consists mainly of a-Si for its active layer.
- poly crystalline silicon or organic semiconductor can be used for the thin-film transistor as its active layer.
- the thin film transistors 221 , 222 and 223 in FIGS. 10A, 10B, 10C and 10D are preferably a-Si type TFTs.
- FIG. 12 shows two pixel circuits 51 a , 51 b , each being in accordance with pixel 200 A of FIG. 10A .
- FIG. 13 shows that scan pulses 53 a , 53 b applied to scan line 52 a of a first pixel circuit 51 a and then scan line 52 b of a second pixel circuit 51 b , and the consequential current 55 a drawn through the signal line 54 .
- the scan pulses are high, the current increases in magnitude, but becomes more negative.
- the predetermined brightness of the luminescence transistor is repetitively set in synchronization with a scan cycle.
- the scan cycle refers to a cycle at which a pulse voltage is applied to a scan line on a regular basis. Every time a pulse voltage is applied, an appropriate pixel brightness setting is updated. This allows a predetermined brightness to be repetitively set in an appropriate pixel.
- FIG. 14 shows a scan pulse 53 a is repetitively applied through the scan line 52 a and the resulting current 55 b in the signal line 54 in synchronization to set the brightness 56 of the first pixel circuit pixel 51 a .
- the signal current 55 b shows an increase in negative magnitude at 53 d due to a pulse on a different scan (eg scan line 52 b ), so does not affect the current brightness signal 56 from pixel circuit 51 a .
- the scan pulse on scan line 54 stops at 53 c , the brightness it mostly sustained until the brightness information is updated at the next cycle.
- This driving method is suitable for high scan rate 30 frames per second or higher.
- FIG. 15 shows an exemplary layout of a pixel for a RGB active matrix colour display, based on a luminescence transistor according to the present invention and using two TFTs in the backplane to drive and control the luminescence transistor.
- the layout shows a scale of 5 ⁇ m line/space.
- This layout achieves an aperture ratio (ie the proportion of the pixel that provides luminescence) of 50%.
- this ratio is significantly larger than 30% ratio generally achievable with FET-type luminescence transistors
- FIG. 16 shows a passive matrix pixel circuit 60 for driving electroluminescent devices in accordance with the present invention.
- the passive matrix pixel circuit 60 includes a plurality of single pixel circuits 60 a .
- Each single pixel circuit 60 a has a first control line (eg a signal line) 61 coupled to an input electrode 40 of the electroluminescent device 100 for setting a voltage at the input electrode, and a second control line (eg a scan line) 62 connected to the electroluminescent device for applying a voltage between an anode and a cathode of the device.
- the first and second control lines are synchronised such that the first control line provides a pulse that controls luminescence emitted from the electroluminescent device.
- the scan lines of each matrix circuit are also connected to a scan controller and the signal lines of each matrix circuit are also connected to a signal controller (not shown).
- a multiplexing drive (not shown) for the passive matrix circuit 60 is configured such that signal controller and scan controller of each circuit are arranged to independently control each pixel circuit.
Abstract
Description
- The present invention relates to light emitting devices, especially transistors which incorporate an organic electroluminescent (EL) element to form an organic light emitting diode (OLED) in the transistor, and methods of manufacturing such devices.
- Advances in OLED technology have in recent times resulted in an effort to manufacture and optimise display devices based on OLED technology. Despite recent progress in OLED technology, there is still a desire to improve the performance of OLED display devices, and the ease and cost of manufacturing such devices. Improving OLED technology will improve the competitiveness of OLED displays compared with inexpensive liquid crystal displays.
- An exemplary OLED display panel having an active matrix structure comprises a matrix of pixel circuits. Each pixel circuit has an OLED device and backplane having matrix wiring and thin film transistors (TFTs) for switching and driving the OLED device.
- Such a pixel circuit has difficulty delivering and controlling electric current passed through each OLED device. This is because each drive TFT is comprised of amorphous silicon (a-Si) which has low carrier mobility. The low carrier mobility prevents a small a-Si TFT from delivering a large drive current. Additionally, such an a-Si TFT suffers from great changes in characteristics when subjected to a continuous current application, making control of the drive current difficult.
- Discussed below are several approaches which have been proposed to address these difficulties.
- A first proposed solution is to use a polycrystalline silicon TFT for the drive TFT. This provides the drive TFT with higher carrier mobility. However, this technology necessitates crystallization annealing processes in order to obtain polycrystalline silicon, generally on a glass substrate. The crystallization annealing is typically conducted through laser heating to temperatures above 1000° C., and it suffers from the disadvantage of a lower throughput as well as lower yield, resulting in a significantly higher cost as compared with a-Si TFT.
- A second proposed solution is to use amorphous oxide TFTs for the drive TFTs. This technology uses a non-crystalline semiconductor of metal oxide, such as an oxide of In or Zn, and accordingly has an advantage of eliminating the necessity for crystallization processes such as a laser annealing process. However, this technology also suffers from the disadvantage of significantly lower yield. The low yield is due to a need for approximately 5-micron rule micromachining. There is also a difficulty in using existing a-Si manufacturing lines to manufacture amorphous oxide TFTs.
- A third proposed solution is to provide a luminescence transistor by giving the TFT a luminescence function, thereby reducing the number of transistors required in the pixel circuit. An example of such an attempt is disclosed in JP2002-246639 where the TFT has a luminescence signal visible as a narrow line on a surface. However, such a TFT suffers from having a narrow emission area. Narrow line emission has limited scope in applications involving display units. Further, it is difficult to separate the luminescence transistor manufacturing process and the backplane manufacturing process.
- A fourth proposed solution is to provide a luminescence transistor that operates based on function as a junction transistor, as opposed to a TFT, which is a field effect transistor. By integrating junction transistor functions and organic EL functions, load on the drive transistor is reduced compared with using a TFT drive transistor.
- A luminescence transistor based on a junction transistor function may be more realistic than a TFT function because unlike a TFT, a junction transistor does not confine current to a narrow channel. Consequently, junction transistor technology can create a pixel having a greater luminescence area than in the case of TFT. Such technology is disclosed in JP2005-293980, JP2006-269323, JP2007-200788, JP2009-272442, and JP2010-135809. Disclosed amongst these documents is a current control base electrode disposed in a middle portion of an organic semiconductor layer, in which the base electrode is a slit-like conductor, a planar conductor, or a conductor/semiconductor having a laminated structure. The disadvantage of these technologies is that a semiconductor layer having a current control base electrode disposed in the middle portion is difficult to manufacture.
- This technology enables the use processes at lower temperatures (eg at or below 300° C.) than in some other technologies, for example in technologies requiring annealing. Such technology therefore has an advantage of allowing a separation between the luminescence transistor manufacturing process and the backplane manufacturing process.
- However, the structure of having a conductor inserted into an organic semiconductor performs poorly as a junction transistor. Furthermore, the structure is unstable, and its instability becomes an impediment to volume production and to production of large panels.
- It would be desirable to solve or at least ameliorate at least one of these problems of the prior art. Various embodiments of the invention may therefore provide a stable, inexpensive, and/or high-performance luminescence transistor or active matrix OLED display. Various embodiments may allow a separation between the luminescence transistor manufacturing process and the backplane manufacturing process, and/or reduce a current control load at the backplane.
- Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.
- In a first aspect of the present invention there is provided an electroluminescent device comprising: an organic electroluminescent element and a junction transistor having a first region, a second region, and an intermediate semiconducting region configured to control flow of charge between the first and second regions. At least two abutting regions consist essentially of one or more semiconducting inorganic metal compounds. Each region of the junction transistor and the electroluminescent element are successively stacked along a common direction.
- Preferably, the electroluminescent device is a luminescence transistor. The luminescence transistor has preferably three electrodes, specifically a first electrode being connected to the intermediate region, a second electrode being connected to either the junction transistor or the electroluminescent element and a third electrode being connected to the other of the junction transistor or the electroluminescent element.
- Preferably, the intermediate semiconducting region is a base region, the first region is an emitter region and the second region is a collector region, the base region and at least one of the emitter region or collector region being abutting regions.
- Preferably, the organic electroluminescent element is distinct from and, more preferably, abuts the junction transistor. However, in other embodiments, one or more layers (e.g. a conducting layer) may exist between, but electrically couple, the electroluminescent element and the junction transistor.
- Preferably, the electroluminescent element and each region of the junction transistor are layers that overlie each other. For example, the regions and junction transistor may each be planar, with each lying in a different plane.
- More preferably, the electroluminescent element and each region of the junction transistor are successively stacked along a vertical direction.
- Preferably, the two abutting regions consist essentially of one or more semiconducting inorganic metal compounds selected from metal oxides, nitrides, sulphides or carbides.
- Preferably, the intermediate semiconducting region and the first region are abutting regions consisting essentially of one or more semiconducting inorganic metal compounds selected from metal oxides, nitrides, sulphides or carbides and the second region comprises one or more charge transporting organic carrier materials or metals. In one embodiment, wherein the second region comprises one or more charge transporting organic carrier materials or metals having a work function <2.5 eV or >4.0 eV.
- Alternatively, the intermediate semiconducting region and the second region are abutting regions consisting essentially of one or more semiconductor materials selected from metal oxides, nitrides, sulphides or carbides and the first region comprises one or more organic materials or metals. In one embodiment, the first region comprises one or more charge transporting organic carrier materials or metals having a work function <2.5 eV or >4.0 eV.
- Preferably, the intermediate and each of the first and second regions consists essentially of at least one semiconducting material. In one or more embodiments, back-to back p-n junctions are respectively created between the first region and the intermediate region and between the intermediate region and the second region, thereby forming a PNP junction transistor or an NPN junction transistor.
- In other embodiments, the intermediate and each of the first and second regions are all formed from n-type or p-type semiconducting material. Addition of a high resistive (insulating) layer to the intermediate region creates a potential energy barrier to the flow of charge between the first and second regions. Adjusting the potential of the intermediate region enables the charge flow to be controlled.
- In all cases, the intermediate semiconducting region is the base, and the first and second regions respectively form either (i) the emitter and collector, or (ii) the collector and emitter of the junction transistor.
- In one embodiment, the intermediate, first and second regions consists essentially of one or more semiconductor materials selected from metal oxides, nitrides, sulphides or carbides.
- In one embodiment, but a schottky diode or schottky junction is additionally included between the intermediate region and the first region and/or between the intermediate region and the second region.
- Optionally, the intermediate region and only one of the first and second regions consist essentially of semiconducting material, and the other of the first and second regions consists essentially of at least one metal forming schottky junction with the intermediate region.
- Preferably, the intermediate semiconducting region consists essentially of one or more semiconducting inorganic metal compounds selected from Zn, Cu, Ru, Al, In, Ga, Sn or Ti oxides.
- In one embodiment, the intermediate semiconducting region has a structure of stacked laminae comprised of two or more layers of semiconductor materials, wherein the two or more layers include a high resistive layer and a low resistive layer.
- In other embodiment, the intermediate semiconducting region consists of a structure where a high resistive layer and a conductive or low resistive layer are laminated to form two layers, thus forming an n-type only or a p-type only junction.
- Preferably, the first region consists essentially of one or more semiconductor materials selected from Zn, Cu, Ru, Al, In, Ga, Sn or Ti oxides.
- Preferably, the second region consists essentially of one or more semiconductor materials selected from Zn, Cu, Ru, Al, In, Ga, Sn or Ti oxides.
- Preferably, the junction transistor is transparent. Preferably, light transmitted though the electroluminescent device is at least 30% of light incident, ie for externally generated light that is incident on the electroluminescent device, at least 30% of that light is transmitted through the device, giving the device a transmittance of at least 30%.
- Preferably, the electroluminescent device is configured such that light is generated from an organic light emission layer within the electroluminescent element, wherein the light emission layer is located between the junction transistor and further layers of the electroluminescent element.
- In one embodiment, the further layers include a hole transport layer and/or an electron transport layer. Preferably, the electroluminescent element further includes a hole injection layer or an electron injection layer.
- It is appreciated that the electroluminescent element, is referred to as being “organic” due to the organic light emission layer, but the element can nonetheless include inorganic layers. For example, it may include an inorganic electron injection layer, such as LiF. Preferably, the electroluminescent element is or includes an organic light emitting diode. However, in other embodiments, the organic electroluminescent element forms only part of an organic light emitting diode, with the other part of the organic light emitting diode being provided by the junction transistor, eg the collector of the junction transistor.
- Optionally, light generated from the light emission layer is transmitted through the junction transistor and is reflected by one or more of the further layers of the organic electroluminescent element.
- Alternatively, light generated from the light emission layer is transmitted through the further layers of the organic electroluminescent element and is reflected by a reflector region located between the junction transistor and a substrate.
- Alternatively, light generated from the light emission layer is transmitted through the junction transistor as well as the further layers of the organic electroluminescent element.
- In a second aspect of the present invention, there is provided a pixel circuit comprising an electroluminescent device, according to the first aspect of the present invention, connected to a control circuit for controlling operation of the electroluminescent device, wherein the control circuit comprises: a switching means; a current setting transistor; and a capacitor.
- Preferably, the switching means is configured to selectively couple a first control line and to an input electrode of the electroluminescent device for setting a voltage at the input electrode when the switching means is on; the current setting transistor is configured to deliver into or draw current out of the electroluminescent device, via said input electrode, when the current setting transistor is in a biased state; and the capacitor is configured to prolong the current setting transistor in the biased state when the switching means is turned off so as to prolong said delivered or drawn current.
- In embodiments where the junction transistor is an NPN transistor the current setting transistor is configured to deliver current into the electroluminescent device, whereas in the cases where the junction transistor is a PNP transistor, the current setting transistor draws current out of the electroluminescent device.
- Preferably, the switching means is a thin film transistor (TFT) having a gate connected to a second control line and source and drain configured for said coupling of the first control line to the input electrode.
- Preferably, the current setting transistor is a TFT having a gate connected to the capacitor.
- Preferably, the switching means additionally selectively couples the first control line to configure the current setting transistor in a biased state when the switching means is on.
- In one embodiment, a second switching means selectively couples the first control line to set the voltage at the input electrode when the switching means is on, wherein the capacitor is isolated from the input electrode.
- In a third aspect of the present invention, there is provided a pixel circuit comprising an electroluminescent device according to the present invention connected to a matrix circuit for controlling operation of the electroluminescent device, wherein the pixel circuit comprises: a first control line coupled to an input electrode of the electroluminescent device for setting a voltage at the input electrode; and
- a second control line connected to the electroluminescent device for applying a voltage between an anode and cathode of the device;
wherein the first and second control lines are synchronised such that the first control line provides a pulse that controls luminescence emitted from the electroluminescent device. - Preferably, a pixel matrix circuit comprises a plurality of said pixel circuits, wherein each electroluminescent device, wherein the second control lines of each pixel circuit are connected to a scan controller and the first control lines of each pixel circuit are also connected to a signal controller.
- Preferably, a multiplexing drive for a pixel matrix circuit as described above, comprises the signal controller and scan controller configured to independently control each pixel circuit.
- In a fourth aspect of the present invention, there is provided a multiplexing drive comprising: at least two of said pixel circuits according to the third aspect of the present invention, wherein the signal controller and scan controller of each circuit is arranged to operate independently.
- In a fifth aspect of the present invention, there is provided an electroluminescent display panel comprising: a front plane and a back plane, the front plane including at least an electroluminescent device according to the present invention, and the back plane including at least a control circuit including at least two TFTs and at least one capacitor.
- Preferably, the TFTs are chosen from polycrystalline Si TFT, amorphous Si TFT, oxide TFT or organic TFT.
- Preferably, the at least two TFTs and the at least one capacitor are configured to form a pixel circuit in accordance with the third aspect of the present invention.
- In a sixth aspect of the present invention, there is provided a method for manufacturing an electroluminescent device in accordance with the present invention, wherein the method includes:
- a) depositing the layers consisting of one or more semiconducting inorganic metal compounds by sputtering; and thereafter
- b) depositing the electroluminescent element by vacuum deposition.
- In a seventh aspect of the present invention there is provided a method of manufacturing an electroluminescent display panel in accordance with the present invention, wherein the backplane is manufactured by at least a process of a first type and manufacturing the front plane includes a process of a second type that is different to the first process.
- Preferably, the first type of process is performed at a temperature between 250-350 degrees C., and the second type of process is performed at a substrate temperature below 200 degrees C. Preferably, the substrate temperature is between room temperature and 100 degrees C.
- Preferably, the second type of process is used to depositing one or more organic layers on, including at least the electroluminescent element, on the layers consisting of one or more semiconducting inorganic metal.
- Preferably, in the method according to the seventh aspect of the invention, the electroluminescent device is manufactured by a method in accordance with the sixth aspect of the invention.
- As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps.
- Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.
-
FIG. 1 is a diagrammatic view of an embodiment of an electroluminescence transistor comprising a PNP junction transistor; -
FIG. 2 is a diagrammatic view of an embodiment of an electroluminescence transistor the same as inFIG. 1 , but having a base comprised of multiple layers; -
FIG. 3 is a diagrammatic view of another embodiment of an electroluminescence transistor comprising an NPN junction transistor; -
FIG. 3A is a diagrammatic view of another embodiment of a PNP electroluminescence transistor in accordance withFIG. 1 or 2 , configured for bottom emission; -
FIG. 3B is a diagrammatic view of another embodiment of a PNP electroluminescence transistor in accordance withFIG. 1 or 2 , configured for top and bottom emission; -
FIG. 4 is a diagrammatic view of another embodiment of a PNP electroluminescence transistor as inFIG. 1 or 2 , but having a reflector and being configured for top emission; -
FIG. 5 is a diagrammatic view of an embodiment of an electroluminescence transistor comprising a NPN junction in accordance withFIG. 3 , configured for top emission;FIG. 6A shows a top view of an exemplary fabrication of a junction transistor in accordance with the present invention; -
FIG. 6B shows a cross-sectional view of section A-A through the junction transistor ofFIG. 6A ; -
FIG. 7A illustrates experimentally derived current-voltage curves for the respective p-n junctions of the junction transistor ofFIG. 6A ; -
FIG. 7B illustrates experimentally derived current-voltage curves illustrating transistor characteristics of the junction transistor ofFIG. 6A ; -
FIG. 8A shows a top view of an exemplary fabrication of a luminescence transistor in accordance with the present invention; -
FIG. 8B shows a cross-sectional view of section A-A through the luminescence transistor ofFIG. 8A ; -
FIG. 8C illustrates experimentally derived luminescence vs bias voltage curves illustrating luminescence characteristics of the luminescence transistor ofFIG. 8A ; -
FIG. 9 shows an display panel having a grid of pixels driving electroluminescence transistors that are in accordance with the present invention; -
FIG. 10A shows an example of pixel circuit for driving a PNP electroluminescence transistor in accordance with an embodiment of the present invention; -
FIG. 10B shows another example of pixel circuit for driving a PNP electroluminescence transistor in accordance with an embodiment of the present invention; -
FIG. 10C shows an example of pixel circuit for driving an NPN electroluminescence transistor in accordance with an embodiment of the present invention; -
FIG. 10D shows another example of pixel circuit for driving an NPN electroluminescence transistor in accordance with an embodiment of the present invention; -
FIG. 11 shows a cross-sectional view through a portion of a display panel having a backplane and a front plane, the front plane having an electroluminescence transistor in accordance with the present invention mounted; -
FIG. 12 illustrates a portion of an active matrix circuit having two pixel circuits, each pixel circuit being in accordance withFIG. 10A , and being connected to the same signal line and different scan lines; -
FIG. 13 illustrates, for the portion of the active matrix inFIG. 12 , the current signal into the signal line when each of the signal lines are successively pulsed to turn on their respective electroluminescence transistors; -
FIG. 14 illustrates, for the portion of the active matrix illustrated inFIG. 12 , the current signal into the signal line and the brightness of light emitted from one of the pixel circuits, when the pixel circuit is iteratively pulsed in successive scan cycles; -
FIG. 15 shows an exemplary layout of a pixel for an active matrix display; -
FIG. 16 shows a passive matrix for an array of electroluminescent devices according to the present invention; -
FIG. 17 is a diagrammatic view of another embodiment of an electroluminescence transistor comprising an N-type only junction transistor; and -
FIG. 18 is a schematic illustration of the semiconductor band structure of the electroluminescence transistor ofFIG. 18 . - An exemplary embodiment of an electroluminescent device according to the present invention is illustrated, schematically,
FIG. 1 . Electroluminescent device in the form ofelectroluminescence transistor 100 consists of an electroluminescent (EL)element 12 stacked on ajunction transistor 11 to form a structure of stacked laminae or layers (referred to herein as “laminated structure” 150). Thelaminated structure 150 sits flush uponsubstrate 1, with each layer being substantially flat and overlying each other. Each layer is stacked successively on the preceding layer, so that each layer progresses the stack along a common direction that is generally orthogonal to a plane in which the preceding layer lies and to the plane in which the substrate lies. Such a configuration results is referred to as ‘vertical’ configuration because during manufacturing the substrate lies in the horizontal plane. - The
junction transistor 11 is comprised of abase 4 is sandwiched between anemitter 3 andcollector 5 to form a stack of semiconductors. In various embodiments described herein, thejunction transistor 11 may have a PNP, NPN, n-type only or p-type only configuration. “P” refers to a p-type semiconductor in which a hole functions as a primary carrier, while “N” refers to an n-type semiconductor in which an electron functions as a primary carrier. A junction structure in which these are alternately joined to one another so as to form three layers are referred to as “PNP” or “NPN”. - In the embodiment of
FIG. 1 , theemitter 3,base 4, andcollector 5, are respectively p-type, n-type, and p-type semiconductors, thus forming a PNP junction. - The
EL element 12 includes ahole transport layer 6, which sits on and makes a low barrier height contact with thecollector 5 of the of thejunction transistor 11. TheEL element 12 has additional layers that are successively stacked upon one another. The layers are, in order, from one end of the stack to the other, thehole transport layer 6, anemission layer 7, anelectron transport layer 8, and anelectron injection layer 9. - The outer ends of the
laminated structure 150, illustrated inFIG. 1 asbottom end 154 andtop end 156 of thelaminated structure 150, respectively, are each in contact withelectrodes - The
electrodes laminated structure 150 with electrical contacts to allow avoltage 158 to be applied acrossstructure 150. A current flows through each of the layers 3-9 when asecond voltage 159 is applied to bias the base such that the base emitter junction is forward biased. In the case of thePNP electroluminescence transistor 100 ofFIG. 1 , in normal use, electric current (in terms of a notional positive charge), flows into theemitter 3 and out of theelectron injection layer 9, the electrode in contact with theemitter 3 acts as an anode, and theelectrode 10 in contact withelectron injection layer 9 acts as a cathode. Current is also drawn from thebase 4, but the current is small compared with the current flowing from theanode 2 to thecathode 10. However, in the case of an NPN transistor current travels in an opposite direction to the PNP transistor. - At least two abutting semiconductor layers of the
junction transistor 11 consist or consist essentially of one or more semiconducting inorganic metal compounds, such as metal oxides. For example thebase 4 and theemitter 3 can consist or consists essentially of one or more semiconducting inorganic metal compounds, such as metal oxides. Thus in one embodiment, ofsemiconductor layers junction transistor element 11, most of the number of the layers and, generally, most of the volume of the junction transistor consists of inorganic material in the form of various metal oxides. Optionally, all of the semiconductor layers 3, 4, 5 oftransistor element 11 and, as a further option, the electrode in contact with the transistor element 11 (ie anode 2, in the case ofFIG. 1 ) may be comprised inorganic material. In one embodiment, each of the semiconductor layers 3, 4, 5 are a metal oxide. - In order to control the voltage of the
base 4, thebase 4 needs to be (or include a layer that is) of low resistance, ie good conductivity (generally less than 100 kΩ/sheet). However, the conductivity of thebase 4 tends to be adversely affected if thecollector 5 is a metal oxide semiconductor. Therefore, it is advantageous for thecollector 5 is in this embodiment consists of organic material, instead of an oxide semiconductor or other inorganic semiconductor. This organic material is also advantageously in contact with theEL element 12. One organic semiconductor that is suitable for thecollector 5 is TcTa. Other suitable organic semiconductors include NPD, TAPC, PDA, TPD and m-MTDATA. - In another embodiment, illustrated in
FIG. 2 , thebase layer 4 of thejunction transistor 11 consists of a structure where a low resistive layer (generally less than 100 kΩ/sheet) and at least one high resistive layer (generally greater than 1MΩ/sheet) are laminated to form two or more layers. More specifically, thebase 4B consists of three layers, in which a low resistive layer 14 is sandwiched between high resistive layer 13, in contact withemitter 3, and a high resistive layer 15, in contact withcollector 5. - The base layer is typically thinner than the emitter or collector, requiring interface control with the emitter or collector and at the same time proper conductivity. For this reason, a structure in which the low resistive layer and high resistive layer are laminated to form two or more layers is an effective option.
-
Base layer 4, and each layers of thebase 4B, contain at least one of Ga, Zn, Cu, Ru, Al, In, and Ti metal oxides. The use of metal oxide chosen from these metals and its manufacturing conditions allow energy levels, carrier density, and P type/N type to be controlled. For example, in the embodiment inFIG. 1 , thebase layer 4 uses a metal oxidized film (N type) obtained by doping ZnO with In to produce a transparent amorphous oxide semiconductor TAOS. An alternative suitable TAOS material is ZnO with In and Ga (IGZO). Other suitable TAOS materials include IZO, IGO and InO. - Since
junction transistor 11 is a PNP type transistor, as would be understood by a person skilled in the art, a small portion of the current that enters theemitter 3 will exit thebase 4, rather than thecollector 5. - In an alternative embodiment, illustrated in
FIG. 3 , the junction transistor 11B is an NPN type transistor, so in that in normal use, flows from the collector to emitter, with a small proportion of the total emitter current comprising a current component that flows into the base and out of the emitter. In this embodiment, theelectroluminescence transistor 100B is a reciprocal the device inFIG. 1 , as the electric current is configured to flow in the opposite direction to that illustrated inFIG. 1 andFIG. 2 . Forelectroluminescence transistor 100B, thebottom face 153 ofcathode 10 abutssubstrate 1, and atop face 155 ofcathode 10 is forms a low resistance contact with thebottom side 154 of the laminated structure 150B.Anode 2 forms a low resistance contact with thetop side 156 of the laminated structure 150B. The layers 6-8 of the EL element 12B can be comprised of the same materials as layer 6-8 ofEL element 12, but with the layers being positioned in the an opposite order. The layers from theanode 2 to collector 5B are therefore, successively,hole transport layer 6,emission layer 7 andelectron transport layer 8. In this embodiment, theanode 2 acts as the hole injection layer for the EL element 12B, and the collector 5B acts as the electron injection layer for the EL element 12B. The collector 5B,base 3B, and emitter 2B, are respectively N-type, P-type and N-type semiconductors, thus forming a NPN junction transistor element 11B. The junction transistor element 11B is mostly inorganic and the N and P semiconductors may be comprised of the same materials as described in relation toEL device 100. Specifically the N and P semiconductor materials are metal oxides as already described herein. For example the, the n-type emitter can be one or more metal oxides selected from Zn, Cu, Ru, Al, In, Ga, Sn or Ti oxides, and the p-type emitter can be one or more metal oxides selected from Zn, Cu, Ru, AL, In, Ga, Sn or Ti oxides. While collector 5B can also be a p-type metal oxide, as in the case ofdevice 100, it is more advantageous for the collector 5B to be an organic semiconductor. Appropriate organic semiconductors for collector 5B include TmPyPB, BPhene, PBD, TAZ, BND, OXD and TPBi. - In an alternative embodiment, illustrated in
FIG. 17 , thejunction transistor 11E is an N-type only transistor. Thebase 4E consists of a structure where a high resistive layer 300 (generally greater than 1MΩ/sheet) and a conductive or low resistive layer 302 (generally less than 100 kΩ/sheet) 302 laminated to form two layers, thus forming an N-type only junction. - A suitable material for use in the high
resistive layer 300 is high resistive ITO, whereas a suitable material for use in the conductive layer is conductive IGZO. [WHAT OTHER MATERIALS ARE SUITABLE?] - In normal use, the high resistive (insulating)
layer 300 creates a potential energy barrier to the flow of charge between theemitter 3 andcollector 5. Adjusting the potential of thebase 4E enables that energy barrier to be overcome and the charge flow to be controlled. - By way of explanation,
FIG. 18 depicts the semiconductor band structure of the electroluminescence transistor ofFIG. 17 . As shown inFIG. 18 , electrons are transported in the highest occupied molecular orbit (HOMO) from thecathode 10, and other electrons are transported in the conduction band from theanode 2. Holes are generated at the PN junction of the interface of the hole transport layer (HTL) 6 and the hole injection layer (HIL) orcollector 5. The holes and electrons from thecathode 10 recombine in theemission layer 7, resulting in the emission of light. The injected current can be regulated by controlling the potential ofbase electrode 4E. - The emitter may be formed from conductive ITO, InO, ZnO, IGZO, SnO. [WHAT OTHER MATERIALS ARE SUITABLE?]
- In an alternative embodiment (not shown), the junction transistor is a P-type only transistor, Once again, the base consists of a structure where a high resistive layer and a conductive or low resistive layer laminated to form two layers, thus forming an P-type only junction.
- The emitter may be formed from conductive CuO, CuAlO [WHAT OTHER MATERIALS ARE SUITABLE?]
- For the NPN, PNP, n-type only and p-type only embodiments described herein, the
electrodes laminated structure 150. The anode, being on the hole-injection end, in some embodiments contains at least one of Ga, Zn, Cu, In, Ti, and Si metal oxide semiconductors. The cathode, being at the electron injection end, in some embodiments contains at least one of Al, Li, Mg, K, Na, Ba, Sr, Ag, Ca and Cs metal or metallic compounds. The use of these materials allows barrier height to be controlled when holes or electrons are injected. - For one embodiment in accordance with
FIG. 1 ,emitter 3 is an inorganic metal oxide semiconductor formed of CuAlO2.Theanode 2 attached to theemitter 3 is comprised of ITO (In, Sn oxide) or mainly ITO. At theelectron injection end 156, Al metal (or mainly Al) is used for thecathode 10, and KF or LiF is used for anelectron injection layer 9. - The Al cathode will reflect light generated from
emission layer 7. However, in this embodiment, thesubstrate 1 is transparent to allow the generated light 160 to be emitted pass through it, as illustrated inFIG. 3A . To allow sufficient light transmission,substrate 1 has a light transmissibility of at least than 50 percent at light wavelength of 400 to 800 nm (ie covering the spectrum of visible light). Thetransistor element 11 is also transparent, and has a light transmissibility of at least 50 percent at light wavelength of 400 to 800 nm. Any light generated from theemission layer 7 oforganic EL element 12 that is falls oncathode 10 is reflected by thecathode 10 and radiated through theglass substrate 1. Therefore the emittedlight 160 is radiated mainly through the transparent substrate. This arrangement is referred to as a bottom emission configuration. Such a structure allows the manufacture oforganic EL element 12 to occur after the fabrication of thejunction transistor 11, thereby preventing the manufacturing processes of thejunction transistor 11 from damaging theorganic EL element 12. - In a variation of this embodiment, the cathode can be made of a transparent material, such as a metal oxide (eg ITO) having transmissibility of at least 50% for visible light, rather than a reflective metal. As illustrated for transistor 100C in
FIG. 3B , this allows light to be emitted from both the top and opposite, bottom side of the transistor. Apart from the requirement of thecathode 10 being transparent, the other components of transistor 100C can be the same astransistor 100. For example transistor 100C can include, for example, LiF for theelectron injection layer 9, TcTa for theCollector 5, ZnO—In for theBase 4, CuAlO2 for theemitter 3, ITO for theanode 2, and glass for thesubstrate 1. - In yet other embodiments, the electroluminescence transistor can be configured to have light emitted only from the end of the electroluminescence transistor on the opposite end to the substrate (ie the top end), as illustrated in the embodiment illustrated in
FIG. 4 (andFIG. 5 ). Such structures are referred to as top emission configurations. -
FIG. 4 illustrates an embodiment of anelectroluminescence transistor 100A having the same features as described in relation to electroluminescence transistor 100C ofFIG. 3B , except that the substrate end of thedevice 100A is reflective rather than transparent, so that light is radiated mainly throughtransparent cathode 10. The reflectivity at the substrate side is provided by achromium reflector 46 between thesubstrate 1 andanode 2. - Another embodiment of a top emission configuration is illustrated in
FIG. 5 for anNPN luminescence transistor 100B consistent withFIG. 3 . In this embodiment, a reflecting surface is provided on the transistor or substrate side of theEL element 12. However, in contrast with the embodiment inFIG. 4 ,luminescence transistor 100B does not require a separate reflector layer. Rather, the junction transistor electrode (cathode 10) in contact with the substrate is a reflective metal, such as aluminium. Theanode 2 at the end opposite the substrate is a transparent material such as an a metal oxide semiconductor (eg ITO), thus allowing light to be emitted primarily from the top of thedevice 100B. -
FIG. 6A andFIG. 6B show a top view and a cross-sectional view, respectively, of an exemplary fabrication of junction type transistor 11C. The fabrication of the junction-type transistor 11C may be adapted to fabricateelectroluminescence transistor 100 by providingEL element 12 andcathode 10, as described in relation toFIGS. 1-3 , in place oftop electrode 25. - Junction transistor 11C has an
anode 21 of ITO having a film thickness of about 150 nm, and abase contact 26. Theanode 21 andbase contact 26 are formed on a glass substrate 20.Emitter 22 is a P-type CuAlO2 film having a film thickness of about 80 nm, which is formed by sputtering on theanode 21. Due to the use of a stencil mask, the area of the film that comprisesbase 23 is limited in area, which limits current from straying laterally and also limits the luminescence region of the substrate 20 (ie, the region from which light is emitted from thebottom 164 of the substrate 20) to a middle portion of the substrate, ie the portion of the substrate 20 that is covered bybase 23. -
Base 23 is formed so as to cover the luminescence region and be in contact with thebase contact 26. The base is a comprised of three n-type layers consisting of a lowerresistive ITO layer 28 sandwiched between lower and upper high resistive ZnO layers, 27 and 29, respectively. Each of the ZnO layers 27, 29 have a film thickness of 15 nm, while theITO layer 28 has a film thickness of 5 nm. The base layers 27-29 are formed by successively sputtering each layer, using a stencil mask. Changing the film thickness of theITO layer 28 allows the conductivity of the base 23 to be adjusted. -
Collector 24 is a P-type organic semiconductor film of TcTa, having a film thickness of about 25 nm.Collector 24 is vacuum-deposited on the base 23 using a stencil mask so as to cover the luminescence region. - Next, an
top electrode 25 comprised of gold is vacuum-deposited. The film thickness of thetop electrode 25 is about 100 nm. - This fabrication of junction transistor 11C has been evaluated for its characteristics.
FIG. 7A shows current-voltage characteristics for the respective p-n junctions formed between theemitter 22 andbase 23, and between thecollector 24 andbase 23. For the base-emitter p-n junction characteristics, a voltage VEB was applied from theemitter 22 to base 23 (ground), via theanode 21 andbase contact 26 electrodes, respectively. Theanode 21 and thebase contact 26 the same voltage as theemitter 22 andbase 23, respectively, due to low resistance contact between theelectrodes respective semiconductors FIG. 7A , VEB is indicated along the x-axis as bias voltage 66, measured in volts. The resulting current fromemitter 22 tobase 23, in milliamps, is indicated bycurve 67, the y-axis indicating current 69 in milliamps. A voltage VBC is similarly applied frombase 23 tocollector 24 by applying voltage tobase contact electrode 26 andtop electrode 25. The resulting current frombase 23 tocollector 24 is indicated bycurve 70. -
FIG. 7B illustrates the results of an experiment in which transistor characteristic curves were derived from operation of junction transistor 11C. The y-axis indicates current, in milliamps, fromemitter 22 tocollector 24 with respect to bias voltage fromemitter 22 to 24 on the x axis. Characteristics curves are illustrated for six different base currents ranging from 0 to −1.0 μA, the negative base current indicating that current is leaving the transistor 11C out ofbase 23. The voltage VEC was applied to measure the dependence of a current IEC on base current IB, showing that the current between theemitter 22 andcollector 24 modulates, depending on the base current IB. -
FIG. 8A andFIG. 8B show a top view and a cross-sectional view, respectively, of an exemplary fabrication ofluminescence transistor 100D. - The substrate 30, anode 31, emitter 32,
base contact 40 and base 33 are formed of the same materials, in the same quantities, and in the same manner as the corresponding substrate 20,anode 21,emitter 22,base contact 26 andbase 23 of junction transistor 11C. - However, in contrast with the junction transistor 11C, the collector 34 is, in this example, an organic semiconductor in the form of HAT, having a film thickness of 2 nm. The HAT organic semiconductor of collector 34 is vacuum-deposited on base 33. The collector 34 of the junction transistor 11D also function as a hole injection layer for the EL element 12D.
- A P-type organic semiconductor film consisting of TcTa and having a film thickness of about 25 nm is vacuum-deposited on the collector 34 to form a hole transport layer 35. Next, mCP and FIrpic are together vacuum deposited on the hole transport layer 35 to form emission layer 36, having a film thickness of about 40 nm. The mCP and FIrpic are deposited in volume proportions of about 94% and 6%, respectively
- Next, an
electron transport layer 37 is provide by vacuum depositing TmPyPB, with a film thickness of about 20 nm, over layer 36. - Each of the collector 34, hole transport layer 35, emission layer 36 and
electron transmission layer 37 are vacuum-deposited using a stencil mask so as to cover the luminescence region. - Next, an
electron injection layer 38 consisting of LiF, with a film thickness of about 1 nm, and thencathode 39, consisting of Al having a film thickness of about 100 nm, are successively vacuum-deposited using a stencil mask so as to cover the luminescence region. The stencil mask is configured to allow thecathode 39 to be formed such that it extends beyond the luminescence region so to provide anoutside electrode portion 39D (FIG. 8A ). - The results of an experiment on
luminescence transistor 100D, are shown inFIG. 8C , illustrating how increases in base current IB modulates an increase in luminescence bright brightness. The y-axis indicates luminescence in cd/m2, and the x-axis indicates bias voltage VAC from the anode 30 tocathode 39, with thecathode 39 being grounded.FIG. 8C illustrates luminescence vs VAC for five values of base current IB, ranging from 0 to −1 μA. -
FIG. 9 depicts an active matrix organic light emitting diode display (AMOLED) 201 comprised of a grid ofpixels 201A. Each pixel includes three pixel circuits, described below, with each circuit having an electroluminescent element in accordance with the present invention (eg electroluminescence transistor 100), respectively configured to emit light in red, green and blue light. Each pixel circuit is addressed by a unique intersection ofhorizontal scan lines 219 a(r, g, b) to 219 n(r, g, b) andvertical signal lines 218 a(r, g, b) to 218 n(r, g, b). Each of the red, green and blue light pixel circuits could be considered sub-pixels of a single pixel. However, for convenience, no distinction is made hereinafter between pixels and sub-pixels—both are referred to as ‘pixels’. -
FIG. 10A is a schematic of a portion of an active matrix display, showing apixel circuit 200A, in accordance with an aspect of the present invention. -
Circuit 200A includes aluminescence transistor 202 such asluminescence transistor 100, or any other p-n-p type electroluminescent transistor in accordance with the present invention. - The
luminescence transistor 202 hascathode 204 and ananode 206 through which current passes from theanode 206 to the cathode 204 (ignoring, for simplicity, a loss of current via the base current). The current passes between an emitter (at anode 206) and a collector of the junction transistor, and through the luminescent element tocathode 204. Theanode 206 is electrically connected directly topower line 210, and thecathode 204 is electrically connected to groundline 212, so that a constantsupply voltage V AC 207, is held on the anode with respect to the cathode, which is equal to the voltage of the power line with respect to the ground line. - The current through the luminescent element is a function of a base current IB into or out of
base 208. For the pixel circuit illustrated inFIG. 10A , the junction transistor element of the luminescence transistor is a PNP-type junction transistor, when base current IB is out of the base 208 when the luminescence transistor is on. Since the junction transistor is a PNP-type, theluminescence transistor 202 will turn on when the voltage ofbase 208 is pulled low (toward the ground line 212), and will be off when the voltage ofbase 208 is pulled high (toward the power line 210). - A switching means in the form of a thin film transistor (TFT) 221 selectively couples a first control line in the form of
signal line 218 a(r, g or b) to thebase 208, and is controlled byscan line 219 a(r, g or b). - When the
signal line 218 a is low and thescan line 219 a is high,TFT 221 is on, pulling the base voltage low drawing current though the base. The current through the base generates a voltage between the emitter and base, which is held by a capacitor. InFIGS. 10A and 10B , thecapacitor 220 is connected between the base 208 and thepower line 210. The voltage at the base will settle to a pre-determined steady-state level, determined by the voltage of the signal line, thereby resulting in a predetermined current through the electroluminescent element of theluminescence transistor 202. Thus results in the emission of light at a predetermined intensity or brightness. The precise current drawn frombase 208 is largely determined by acurrent setting transistor 222 which has its gate and either its source of drain coupled to thebase 208, which the other of the source or drain being connected to groundline 212. Thecurrent setting transistor 222 thus acts as a current source, pulling current from the base 208 to ground. - When the
scan line 219 a is pulled high,TFT 221 turns off. However, thecapacitor 220 keeps the voltage that the gate ofcurrent setting transistor 222 is a biased state such that the same level of current continues to be pulled frombase 208, and therefore the predetermined illumination level of theluminescence transistor 202. - As time passes, the
capacitor 220 will gradually discharge due to the resistance betweenbase 208 and theanode 206 of theluminescence transistor 202, connected across thecapacitor 220. - Thus the base voltage will gradually increase until the electroluminescent transistor turns off on the current setting transistor is no longer draws current from the
base 208. However, the presence of the capacitor prolongs the on-time of thetransistor 202, compared to the same circuit without the capacitor. - An alternative
exemplary pixel circuit 200B (FIG. 10B ) is the same aspixel circuit 200A, except that the switchingtransistor 221 that is connected to the base of the electroluminescent device is disconnected from the capacitor and current setting transistor. Asecond switching transistor 223 independently couples the signal line to the capacitor and the gate of the current setting transistor. In this manner, when the scan line goes high and switchingtransistors - The configuration in
FIG. 10B , can be summarised as providing a pixel configuration constituting a display that includes the luminescence transistor, at least two thin-film transistors, and at least one capacitor and holds the gate voltage of one of the thin-film transistors through the electric voltage generated by an electric current that is passed through the base of the luminescence transistor and thereby gives a predetermined brightness, wherein the source or gate electrode of the thin-film transistor is connected to the base layer of the luminescence transistor, and one terminal of the capacitor is connected to the gate electrode of the thin-film transistor, and the gate voltage of the thin-film transistor is determined by a voltage given from a signal line, and, at the same time, is held by electrical charge stored in the capacitor and, in addition, an electric current flowing through the base layer of the luminescence transistor is held, thereby setting a predetermined brightness. - In both of these configurations in
FIGS. 10A and 10B , the gate voltage of current control transistor is set by an electric voltage that is generated between the base and the emitter of the luminescence transistor as a result of the current passed through the base of the luminescence transistor. The luminescence transistor can thereby be biased to give a predetermined brightness level. - With this arrangement, a predetermined brightness level is set in the luminescence transistor and held until a new brightness level is set by the voltage level of the signal line, at the next scan cycle.
- This base current setting method has an advantage in the ability to provide highly reproducible light emission despite variation in electrical characteristics of the luminescence transistor. JP2008-171580 discloses a pixel circuit in which a luminescence transistor is driven by one or two TFTs, but in contrast with the pixel circuit in
FIG. 10A , the pixel circuit cannot hold the gate voltage of the thin-film transistor through the electric voltage generated by an electric current that is passed through the base. - The above pixel circuits can be modified to operate on an n-p-n type luminescence transistor (
eg luminescence transistor 100B), as illustrated inFIGS. 10C and 10D . The functions of each of the circuit components is the same as inFIGS. 10A and 10B , but with some variations in the topology. In the n-p-n case, the emitter of the luminescence transistor is on the ground line side of the circuit of the circuit, as opposed to the power line side in the p-n-p case. Thus the luminescence transistor turned on by pulling its base electrode high. Therefore, the positions of the capacitor and the current setting resistor are revered compared to the p-n-p case, such so in the n-p-n case the capacitor is connected between the base and ground and the current setting transistor is located between the base and the power line. The luminescence transistor is turned on when the signal and scan lines are high, driving current into the base. The luminescence transistor is off, when the scan line is low. - The pixel circuit of
FIGS. 10A, 10B, 10C and 10D is formed such that the active capacitors, switching transistor(s) and current setting transistor are formed in a planarization layer 18 (FIG. 11 ) on asubstrate 1. Thesubstrate 1 can be transparent under visible light so that light can be transmitted through the substrate (eg a bottom emission configuration). This structure has an advantage of enabling a separation between the manufacturing process of abackplane layer 16 having the switching and current setting TFTs (only oneTFT 19 is shown), the capacitor (not shown) and matrix wiring, and the manufacturing process of aseparate layer 17 having the luminescence transistor. It is appreciated, however, that a more basic control circuit may be employed so that the backplane layer includes, for example only one TFT (ie switching transistor 221), as shown inFIG. 11 , rather than the two or three transistors and a capacitor as in the pixel circuits ofFIGS. 10A-10D . - In any case, the planarization of the backplane his is particularly beneficial because, the backplane can be manufactured using existing manufacturing facilities, so investment is only required to develop manufacturing facilities for the luminescence transistor itself.
- In the present invention, a configuration having such a two-layer structure is particularly effective in pixel configuration in cases where the thin-film transistor includes an active layer consisting mainly of non-crystalline silicon or metal oxide. This is because technologies already established as mass production processes can be used. Accordingly, in the embodiment illustrated in
FIG. 11 , the thin-film transistor consists mainly of a-Si for its active layer. However, alternatively, poly crystalline silicon or organic semiconductor can be used for the thin-film transistor as its active layer. Similarly, thethin film transistors FIGS. 10A, 10B, 10C and 10D are preferably a-Si type TFTs. -
FIG. 12 shows twopixel circuits 51 a, 51 b, each being in accordance withpixel 200A ofFIG. 10A .FIG. 13 shows that scanpulses 53 a, 53 b applied to scan line 52 a of a first pixel circuit 51 a and then scan line 52 b of asecond pixel circuit 51 b, and the consequential current 55 a drawn through the signal line 54. When the scan pulses are high, the current increases in magnitude, but becomes more negative. - As was discussed above, the predetermined brightness of the luminescence transistor is repetitively set in synchronization with a scan cycle.
- The scan cycle refers to a cycle at which a pulse voltage is applied to a scan line on a regular basis. Every time a pulse voltage is applied, an appropriate pixel brightness setting is updated. This allows a predetermined brightness to be repetitively set in an appropriate pixel.
-
FIG. 14 shows ascan pulse 53 a is repetitively applied through the scan line 52 a and the resulting current 55 b in the signal line 54 in synchronization to set thebrightness 56 of the first pixel circuit pixel 51 a. The signal current 55 b shows an increase in negative magnitude at 53 d due to a pulse on a different scan (eg scan line 52 b), so does not affect thecurrent brightness signal 56 from pixel circuit 51 a. When the scan pulse on scan line 54 stops at 53 c, the brightness it mostly sustained until the brightness information is updated at the next cycle. This driving method is suitable for high scan rate 30 frames per second or higher. -
FIG. 15 shows an exemplary layout of a pixel for a RGB active matrix colour display, based on a luminescence transistor according to the present invention and using two TFTs in the backplane to drive and control the luminescence transistor. The layout shows a scale of 5 μm line/space. This layout achieves an aperture ratio (ie the proportion of the pixel that provides luminescence) of 50%. Advantageously, this ratio is significantly larger than 30% ratio generally achievable with FET-type luminescence transistors -
FIG. 16 shows a passivematrix pixel circuit 60 for driving electroluminescent devices in accordance with the present invention. The passivematrix pixel circuit 60 includes a plurality ofsingle pixel circuits 60 a. Eachsingle pixel circuit 60 a has a first control line (eg a signal line) 61 coupled to aninput electrode 40 of theelectroluminescent device 100 for setting a voltage at the input electrode, and a second control line (eg a scan line) 62 connected to the electroluminescent device for applying a voltage between an anode and a cathode of the device. The first and second control lines are synchronised such that the first control line provides a pulse that controls luminescence emitted from the electroluminescent device. The scan lines of each matrix circuit are also connected to a scan controller and the signal lines of each matrix circuit are also connected to a signal controller (not shown). A multiplexing drive (not shown) for thepassive matrix circuit 60 is configured such that signal controller and scan controller of each circuit are arranged to independently control each pixel circuit. - It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.
Claims (40)
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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AU2013902072 | 2013-06-07 | ||
AU2013902072A AU2013902072A0 (en) | 2013-06-07 | Electroluminescent devices | |
AU2013902125 | 2013-06-12 | ||
AU2013902125A AU2013902125A0 (en) | 2013-06-12 | Electroluminescent devices | |
PCT/AU2014/000595 WO2014194372A1 (en) | 2013-06-07 | 2014-06-06 | Electroluminescent devices |
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US20160126504A1 true US20160126504A1 (en) | 2016-05-05 |
US9882171B2 US9882171B2 (en) | 2018-01-30 |
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US14/896,120 Expired - Fee Related US9882171B2 (en) | 2013-06-07 | 2014-06-06 | Pixel matrix circuit |
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US (1) | US9882171B2 (en) |
JP (1) | JP2016528664A (en) |
KR (1) | KR20160018693A (en) |
WO (1) | WO2014194372A1 (en) |
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CN113571666A (en) * | 2021-07-22 | 2021-10-29 | 京东方科技集团股份有限公司 | Display panel, preparation method thereof and display device |
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GB202013414D0 (en) * | 2020-08-27 | 2020-10-14 | Ams Sensors Singapore Pte Ltd | Light replication/retransmission apparatus and method |
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DE102004002587B4 (en) * | 2004-01-16 | 2006-06-01 | Novaled Gmbh | Image element for an active matrix display |
JP4900160B2 (en) * | 2007-09-26 | 2012-03-21 | 大日本印刷株式会社 | Light emitting element and light emitting display device |
TW200939867A (en) * | 2008-03-14 | 2009-09-16 | Univ Nat Chiao Tung | Display apparatus using array of passive organic LED |
JP5804732B2 (en) * | 2011-03-04 | 2015-11-04 | 株式会社Joled | Driving method, display device, and electronic apparatus |
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- 2014-06-06 JP JP2016517098A patent/JP2016528664A/en active Pending
- 2014-06-06 US US14/896,120 patent/US9882171B2/en not_active Expired - Fee Related
- 2014-06-06 KR KR1020167000318A patent/KR20160018693A/en not_active Application Discontinuation
- 2014-06-06 WO PCT/AU2014/000595 patent/WO2014194372A1/en active Application Filing
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US5528397A (en) * | 1991-12-03 | 1996-06-18 | Kopin Corporation | Single crystal silicon transistors for display panels |
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US9882171B2 (en) | 2018-01-30 |
KR20160018693A (en) | 2016-02-17 |
WO2014194372A1 (en) | 2014-12-11 |
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